Patent Application
20120027582
The disclosure relates generally to rotary turbomachines, and more particularly, to a floating packing ring assembly for use in a turbomachine to avoid transient rubs.
In rotary machines such as turbines, seals are provided between rotating and stationary components. For example, in steam turbines, it is customary to provide a plurality of arcuate packing ring segments to form an annular labyrinth seal between the stationary and rotating components. Typically, the arcuate packing ring segments (typically, four to six per annular seal) are disposed in an annular groove in the stationary component concentric to the axis of rotation of the machine and hence concentric to the sealing surface of the rotating component. Each arcuate seal segment carries an arcuate seal face in opposition to the sealing surface of the rotating component. In labyrinth type seals, the seal faces carry a radially directed array of axially spaced teeth, which teeth are radially spaced from an array of axially spaced annular teeth forming the sealing surface of the rotating component. The sealing function is achieved by creating turbulent or flow restriction of an operative fluid, for example, steam, as it passes through the relatively tight clearances within the labyrinth defined by the seal face teeth and the opposing surface of the rotating component.
The ability to maintain proper clearances without physical contact between the rotating equipment and stationary components allows for the formation of an effective seal. If this radial clearance between the seal faces of the segments and the opposing seal surfaces of the rotating component becomes too large, less restriction is produced and the sealing action is compromised. Conversely, if the clearance is too tight, the sealing teeth may contact the rotating element, with the result that the teeth lose their sharp profile and tight clearance and thereafter create less restriction, likewise compromising the sealing action.
In order to create and maintain a desired seal and to avoid damage to the rotor and packing ring during transient conditions, positive pressure, variable clearance packing rings may be used, for example, a packing ring as disclosed in U.S. Pat. No. 7,384,235 in which a spring assembly is provided which retracts the packing rings radially in and out of the rotor to maintain clearances.
A packing ring assembly for use between a rotating and a stationary component in a turbomachine is disclosed, the assembly including an arcuate packing ring casing, an arcuate packing ring segment positioned at least partially within the packing ring casing, and a resistance component configured to allow movement of the packing ring segment in an axial direction, relative to the rotating component, between a first and second position in response to a pressure condition. In one embodiment, the resistance component allows movement when the pressure condition comprises approximately 30% of the turbomachine load. Also disclosed is an altered surface topography of the rotating component to accommodate variable length teeth extending from the packing ring segment, such that when the packing ring segment is in the first position, a clearance between the packing ring segment and the rotating component is larger than when the packing ring segment is in the second position.
A first aspect of the disclosure provides a packing ring assembly for use between a rotating and a stationary component in a turbomachine, the assembly comprising: an arcuate packing ring casing having an annular groove; an arcuate packing ring segment having a mounting portion and a sealing portion, wherein the mounting portion is positioned at least partially within the annular groove and the sealing portion is proximate to the rotating component; and a resistance component configured to allow movement of the packing ring segment in an axial direction, relative to the rotating component, between a first and second position in response to a pressure condition.
A second aspect of the disclosure provides a turbomachine comprising: a substantially cylindrical rotating component; and a stationary component including a packing ring assembly, the packing ring assembly comprising: an arcuate packing ring casing having an annular groove; an arcuate packing ring segment having a mounting portion and a sealing portion, wherein the mounting portion is positioned at least partially within the annular groove and the sealing portion is proximate to the rotating component; and a resistance component configured to allow movement of the packing ring segment in an axial direction, relative to the rotating component, between a first and second position in response to a pressure condition.
The illustrative aspects of the present disclosure are designed to solve the problems herein described and/or other problems not discussed.
These and other features of this disclosure will be more readily understood from the following detailed description of the various aspects of the disclosure taken in conjunction with the accompanying drawings that depict various embodiments of the disclosure, in which:
It is noted that the drawings of the disclosure are not to scale. The drawings are intended to depict only typical aspects of the disclosure, and therefore should not be considered as limiting the scope of the disclosure. In the drawings, like numbering represents like elements between the drawings.
Turning to
Packing ring segment 20, shown in
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Sealing portion 114 can further include at least one sealing member 117 that extends in a radial direction from packing ring segment 110 towards rotating component 102.
Packing ring assembly 100 further includes a resistance component 118 for allowing movement of packing ring segment 110 in an axial direction, relative to rotating component 102. In one embodiment, resistance component 118 is positioned in annular groove 108, between mounting portion 112 of packing ring segment 110 and downstream inside axial face 128 of annular groove 108. Resistance component 118 may be positioned within annular groove 108 by coupling it to either mounting portion 112 or packing ring casing 106, or both. As such, resistance component 118 can at least partially support packing ring segment 110 because as a portion of resistance component 118 is attached to packing ring casing 106, and a portion of resistance component 118 is attached to mounting portion 112, mounting portion 112 will be suspended, i.e., floated, within annular groove 108. Packing ring assembly 100 is referred to as a “floating” seal arrangement because packing ring 110 can be positioned, i.e., ‘floated’, in an axial direction in packing ring casing 106 due to a pressure of the operating fluid flowing through the turbomachine and a stiffness of resistance component 118. Any known means of attaching resistance component 118 can be used, including welding, brazing, adhesive bonding, diffusion bonding, mechanical joining including but not limited to dovetail joints, mortise and tendon joints, flexible and sliding joints, threaded holes, screws or nuts or bolts.
Resistance component 118 can comprise any known means that can be configured to allow packing ring segment 110 to move axially between a first and second position, relative to rotating component 112. Suitable means can include a hydraulic, pneumatic or electromagnetic resistance component that is configured to compress, or move, in response to a pressure condition, to allow packing ring segment 110 to move in an axial direction. For example, as discussed in more detail herein,
As discussed herein, resistance component 118 can be configured such that, in response to a pressure condition in annular groove 108, resistance component 118 allows packing ring segment 110 to move in an axial direction. In one embodiment, this pressure condition can be passively controlled. For example, packing ring casing 106 can further include at least one opening 120 extending from upstream axial face 122 of packing ring casing 106 to upstream inside axial face 126 of annular groove 108, wherein opening 120 is configured to allow operating fluid, OF, of the turbomachine to travel through opening 120 into annular groove 108 to contact mounting portion 112 of packing ring segment 110. Opening 120 can comprise an opening or hole of any desired shape or configuration and can be positioned in packing ring casing 106 as desired.
As operative fluid (OF) of the turbomachine travels through opening 120 (illustrated by arrow “OF” in
Turning to
Turning back to
The movement of packing ring segment 110 in an axial direction as discussed herein allows variable length teeth 116a, 116b and rotating component 102 with a variable surface topography to interact in a way that provides a sealing arrangement between packing ring segment 110 and rotating component 102. As shown in
This movement of the packing ring segment 110 axially between a first position as shown in
In another embodiment, the pressure condition within annular groove 108 can be actively controlled to move packing ring segment 110. In other words, the pressure condition can be manipulated to be a certain pressure, rather than relying on the natural flow of the operating fluid through opening(s) 120 to create the pressure condition. For example, as shown in
Fluid bypass system 129 can comprise a series of pipes or conduits configured to direct the operating fluid of the turbomachine around packing ring segment 110. For example, as shown in
At least one bypass control valve 136 is located between inlet 132 and outlet 134 for controlling flow through fluid bypass system 129. Valve 136 may be operated manually or automatically. Automatic operation can be either direct or in conjunction with a machine controller. When valve 136 is open, fluid bypass system 129 offers significantly less resistance to flow as compared to the leakage between sealing members 117 and rotating component 102. This results in a significant reduction in pressure drop across packing ring segment 110. An example of an actively activated fluid bypass system is disclosed in U.S. Pat. Pub. No. 2008/0169616.
A labyrinth seal is shown in the figures herein to illustrate embodiments of this invention, but as one of skill in the art would understand, packing ring assembly 100 disclosed herein can be used on any type of seal used between rotating and stationary components in a turbomachine, including but not limited to brush seals, leaf seals, finger seals, compliant plate seals, shingle seals, honeycomb seals and abradable seals.
The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the disclosure. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and/or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof.
The corresponding structures, materials, acts, and equivalents of all means or step plus function elements in the claims below are intended to include any structure, material, or act for performing the function in combination with other claimed elements as specifically claimed. The description of the present disclosure has been presented for purposes of illustration and description, but is not intended to be exhaustive or limited to the disclosure in the form disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the disclosure. The embodiment was chosen and described in order to best explain the principles of the disclosure and the practical application, and to enable others of ordinary skill in the art to understand the disclosure for various embodiments with various modifications as are suited to the particular use contemplated.
